To make an electrical interconnection between circuit substrates themselves or between electronic parts such as IC chips and a circuit substrate, an adhesive or an anisotropic conductive adhesive with conductive particles dispersed therein is used. More specifically, the electrical interconnection can be made by providing any of these adhesives between electrodes facing each other, connecting the electrodes by heating and pressing and thereafter imparting a conductivity in the direction of pressing. For example, Japanese Patent Application Laid-open No. 3-16147 discloses an adhesive for connecting circuits which is basically comprised of epoxy resin.
However, conventional adhesives making use of epoxy resin as base resin have a problem that, when reliability tests such as a thermal shock test, a PCT test and a solder bath immersion test are made, the connection resistance may become great or the adhesive may come apart at the joints because of internal stress ascribable to a difference in coefficient of thermal expansion of the connecting substrates.
Especially when chips are directly mounted on a substrate through an adhesive, the chips and substrate tend to warp because of internal stress ascribable to a difference in coefficient of thermal expansion between them when a printed substrate making use of an FR-4 base material or a flexible wiring board comprised of a polyimide or polyester base material is used as the connecting substrate.